Electrical resistor



Patented Nov. 4, 1952 i 1 I UNITED STATES PATENT OFFICE ELECTRICAL RESISTOR V Evert Johannes Willem Verwey, Eindhoven, N ethe'rlands, assignor, by mesne assignments, to

Hartford National Bank and Trust Company, Hartford, Conn., as trustee No Drawin Application April 8, 1946, Serial'No.

660,423. In Belgium March 16, 1945 Section I PubIic' Law 690, August 8, 1946 Patent expires March 16, 1965 4- Claims. (01. 252-490) For the manufacture of, electric resistances of about 500 C. If this condition is fulfilled any there were described different combinations of separation of a second phase at temperatures Fe3O4 with other double-oxides of the spinel type over 500 C., which; would produce undesirable according to the formula: R O. R2 O;, in which variations in the resistance properties, cannot R 1 is a bivalent and Rm is a trivalent element 5 occur. At lower temperatures the speed of sep- Furthermore it is. known that with high load aration is so small that no dimculty is encounparticularly stable resistancesmay beobtained by tered in this respect. a y a I converting combinations of Products of a lower temperature coeiiicient p u, may be obtained if more than approximately half 0 Feo*Fe2O3Mg9 A12O3 of the spinel phase consists of FesOi molecules. n a s'int r ed mass wh c s of As the conductivity owing to the high percentage homo e eous sp Ip a -a' dw ch s not o of F9304, greatly increases it may in this case saturated with a secondpha 'at' a e p be desirable to influence the specific resistance of about 500 C. by the presence of a secondph'ase. For this pur- A a b chO s.m op t r y in pose use may be made, .for example, of semithe manufac of products according 0 the conductive or insulating compoundswhich do not last-mentioned proposal was the high sinterins' dissolve or dissolve only with difficulty in the temperature of from 1500 to 1600 C.,- which was spinel phase, for example Mgo and ZIOz.

troublesome in practice By" the'us'e offusing For'the'manufactur'e of resistances according a e t is awba 011 13 be v a V y to the invention the required material is finely well without detrimentally affecting the resist- 7 divided and intimately mixed-and subsequently ance properties and more particularly the stagiven the'd'esired shape ing-a manner customary bility. in ceramic technics, whereafter sintering to; com- It is true that accord n o h' f p p al pactness' may be 'efiected at a temperature of the sintering temperature may b'e reduced to about 1300* C. The conditions inthe sintering about l400 C. by substitution Crzoc for A1203 in and coolingvprocesses, that is to say the temperthe combination of FeO Fe2O3 -MgO- A 12Os ature' and the partial pressure of the oxygen in but this temperature, too, is still disturbingly the surrounding gas as well as the composition high especially in view of the requ-irements which of the initial inixtu'rearechosen to be such that the furnaces have in this case: to satisfy with themolecula'r ratio of the FeaOli to the other manufacture on a large sca1e.- I spinelsinithe mass' is adjusted-in connection with The present invention purports further to the resistance properties'desired. In-order that reduce the sintering tmperaturewhilst obtainduring the subsequent cooling process this ratio ing a product equivalent'to that according to-the may be retained aswell'aspossible, the cooling two last-mentioned proposals. process may be effected rapidlywhilst driving According to the invention,, the conductive out the atmosphere containing oxygen 'by means material of the resistances consists to this end of a relatively inert gas such as nitrogen.- The of mixed crystals of FesOiwith a spinel of the material may alsobe s-intered inan atmosphere type 2R OR O2, in which formula R repre in which the partial pressure" of the oxygen sents a bivalent and R a-tetravalent element- 40 decreases with temperature, i.e. an atmosphere AS Such y be m t n 9111 titanates and Stanof nitrogen" containing superheated water vapor nat s with sp l stru r f xample M z i i, which i qis'soeiable intc x' en" and hydrogen, Zn2TiO4, NizTiOr and ZneSnOi or theirmixed the rate of-dissociation being'dependentupon the crystals temperature? p The resistance value as well as the temperature: lsinee" the content of, FeOi and hence the coefficient' of resistances thus: composed maybe molecular ratioFeO) reset may 'beadjust'ed by adjusted by the choice "offtheucontent' Of FeQO i: the choice of the sintering temperature" and of and the presence, ifuanyn of asecondphase in the the sinteri-nge atmosphere; the initial material sinteredl producin 2 used aforithei'resistances; according to the inven- As regards the temperature coeflicient it may 5,9 tion may be" any-forms of iron oxide and, if 3 be mentioned that this is highly negative in proddesired, iron powder, while the other constituents ucts consisting of a homogeneous spinel phase already referred to above may be used wholly or of which less than approximately half is built in part in the form of double-oxides. up from F3304 molecules and which is not over- Besides, it is of particular advantage that, saturated with a second phase at a temperature owing to the circumstance already favourable per se that the sintering temperature may be reduced to approximately 1300 0., the sintering process may be carried out in an atmosphere of pure nitrogen without the F8304 formed from F8203 being reduced further to the FeO. Thus the reproducibility of the resistance value is also very high. '7

Furthermore, the difliculties encountered in the manufacture of resistances according to the previous proposals are materially decreased. Thus, for example, the use of electric furnaces having a molybdenum winding in a protecting gas is possible since the latter at an operating temperature of approximately 1300 C. have a satisfactory period of life which is appreciably higher than at temperatures of approximately 1400 C. which had to be applied in sintering resistances on basis of F8304 and magnesium chromite. Such advantages also occur with furnaces of any other type.

Owing to the circumstance that according to the invention, a product of high compactness is obtained, the resistances exhibit even with high load a particular stability which is equivalent to that of the above-mentioned resistances manufactured on basis of F6304 and magnesium spinel or magnesium chromite.

The resistances according to the invention may be utilized, for example, for the suppression of current impulses, the stabilisation of the voltage or the compensation of the temperature coefficient of a circuit and, besides, for measuring temperatures.

Example I 0.375 gram-molecules of FezOa 1.5 gram-molecules of N temperature at the hottest place is about 110 C. These resistances are suited, for example, to taking up current impulses...

WhatIclaim Q 1 1. An electrical resistance having a negative temperature coefiicient of resistance consisting of 0.75 gram-molecules of T102 are ground with 7 22000 ohms cm. at 22 C., 900 ohms cm. 138 C. 200 ohms cm. 227 C., 50 ohms cm. 332 C.

The resistances thus manufactured are suitable, for example, for measuring temperatures.

Example II 4.5 gram-molecules of FezO;

10.2 gram-molecules of ZnO 5.1 gram-molecules of TiOz are ground with ethyl acetate for 16 hours and with the use of a 10% nitrocellulose solution in ethyl glycol extruded into tubes of 6.3 mms. long having an external diameter of 8 mms. and an internal diameter of 4.5 mms. Subsequently,

the tubes are heated at 1320 C. in a furnace of 30 cms. length at a travelling speed of 1 cm. per minute whilst using a flow of pure nitrogen (oxygen content about 0.1%) of 5 litres per minute.

The resistance value of the tube unloaded is 1600 ohms, whereas with a load of 100 milliamps. it decreases to 81 ohms. With this load the essentially mixed crystals constituted by 25 to 50 mol of FeaO4 and the balance a spinel having the formula 2R O-R O2, R being a bivalent metal selectedfrom the group consisting of nickel and,zinc and B being a tetravalent metal selected from the group consisting of titanium and tin.

2. An electrical resistance having a negative temperature coefficient of resistance consisting of essentially mixed crystals. constituted by about 25 mol of F6304 and the balance ZNiO-TiOz.

3. Anelectrical resistance having a negative temperature coefiicient of resistance consisting essentially of mixed crystals constituted by about 37% mol of F6304 and the balance 2ZnO-Ti02.

4. A method of manufacturing an electrical resistance having a negative temperature coefiicient which comprises the steps of mixing about 25 to 50 mol of F6304 and 50 to mol of a spinel having the formula 2R O-R Oz, R being a metal selected from the group consisting of nickel and zinc, and R being a metal selected from the group consisting of titanium and tin, said spinel being formed by jointly heating the oxide of a metal of the first group with the oxide of the metal in the second group in the ratio of two mols of the former to one mol of the latter, and sintering the mixture in a nitrogen atmosphere at about 1300 C. for a sufficient time to produce mixed crystals constituted by about 25 to 50 mol of F6304 and the balance said spinel.

EVERT J OHANNES WILLEM VERWEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 648,518 Och May 1, 1900 860,997 Steinmetz July 23, 1907 1,911,396 Saklatwalla et al. May 30, 1933 2,027,277 Habann Jan. 7, 1936 2,068,294 Korinth et al Jan. 19, 1937 2,370,443 Biefeld Feb. 27, 1945 2,371,660 Wainer Mar. 20, 1945 2,418,467 Ellis Apr. 8, 1947 2,468,458 Padmos et a1 Apr. 26, 1949 2,475,864 Verwey et al. July 12, 1949 FOREIGN PATENTS Number Country Date 506,964 Great Britain 1939 OTHER REFERENCES Kawai-Studies on FerritesJournal of the Soc. of Chem. Ind., Japan, vol. 37, No. 4, pg. 1743, pub. 1934.

Mellor Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 13, pg. 732, pub. Longmans, Green & 00., N. Y., 1934. 8 "Iiiackhs Chem. Dictionary, 2nd Ed. 1937, pg. 

1. AN ELECTRICAL RESISTANCE HAVING A NEGATIVE TEMPERATURE COEFFICIENT OF RESISTANCE CONSISTING OF ESSENTIALLY MIXED CRYSTALS CONSTITUTED BY 25 TO 50 MOL % OF FE3O4 AND THE BALANCE A SPINEL HAVING THE FORMULA 2RIIO.RIVO2, R22 BEING A BIVALENT METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND ZINC AND RIV BEING A TETRAVALENT METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND TIN. 